The invention concerns a rotational movement transmission device and an adjustment system for a motor vehicle seat comprising such a device.
Rotational transmission devices are known which comprise a flexible shaft and a casing inside which the shaft is housed. In these transmission devices, in particular for motor vehicle seat adjustment, the speeds of rotation of the shaft in the casing are greater than 2000 revs/minute, conventionally of the order of 3000 revs/minute. In order to allow rotation at such speeds, a gap of a few tenths of a millimeter is necessary between the shaft and the casing. But, during rotation, this gap leads to the appearance of small-amplitude vibrations which propagate along the shaft and cause unpleasant noise and feeling to the touch.
In order to solve this vibration problem, the document JP 07 310 730 proposes a rotational transmission device whose casing has at least one deformation in the form of a constriction, that is to say a local reduction in the diameter of the casing. This is because this constriction, by causing a gripping contact between the shaft and the casing, makes it possible to limit the vibrations. However, this contact creates considerable friction between the shaft and the casing, which requires the motor torque to be increased to obtain a speed of rotation of the shaft sufficient for the envisaged application. Moreover, this friction leads to premature wear of the casing at the deformation.
The invention aims to overcome these drawbacks by proposing a rotational movement transmission device whose casing has permanent deformations which are arranged to limit the vibrations without reducing the internal diameter of the casing. To that end and according to a first aspect, the invention concerns a rotational movement transmission device comprising a flexible shaft and a casing inside which the shaft is housed, said casing being formed from a hollow body of plastic material whose internal diameter is arranged to allow the rotation of said shaft inside said casing, the wall of the body having a variable thickness so that part of the casing has an internal surface comprising corrugations extending longitudinally.
According to a second aspect, the invention concerns an adjustment system for a motor vehicle seat, comprising at least one adjustment runner mounted on the structure of the vehicle and adjustable means for fixing the seat on said runner, said system also comprising a drive motor having at least one revolving part, said adjustment system also comprising a transmission device as described above, which is disposed between the output of said drive motor and said fixing means, so as to move said fixing means along said adjustment runner in response to a rotation of said output. Other objects and advantages of the invention will emerge during the following description, given with reference to the accompanying drawings.